In the manufacture of electrical and electronic components from wafers, it is often necessary to provide sensitive component structures with a cover while they are still on the wafer, i.e., prior to their being separated into individual components. This cover can, for one thing, serve as protection against external influences further along in the manufacturing process or can become the foundation for certain packaging technologies. A cover of this type can form a mechanical protection against media introduced further along in the process or as a protection against contamination, in particular against electrically conductive particles, which are particularly disruptive in miniaturized components. The packaging can be completed based on this cover, for example in a resin mold, compressing it in plastic, installing it in another housing, etc.
Surface acoustic wave devices have especially sensitive component structures that can include inter-digital transducers and reflectors in the form of finely structured conduction paths. These sensitive structures are not, in general, permitted to come into contact with the covers noted above, since this contact can cause properties of the surface acoustic wave devices to change in an unreliable and non-reproducible manner. To cover such structures requires an encapsulation that forms a cavity over the structures.
From WO 95/30 276, an encapsulation for electrical and electronic components is known that comprises a frame and a support structure that encloses the component structures and a cover layer that sits on top of them that can form a hermetically sealed cap, together with the frame, that encloses the sensitive structures. It is preferred that both the frame structure as well as the cover layer be made of a photoresist material, and particularly of a photoresist foil. These are laminated over the entire surface, exposed via a mask, and developed. These steps are separately carried out for the frame structure and the cover layer. Overall, the process is relatively intensive and requires a multitude of process steps.
This embodiment is directed to the encapsulation of active, and thus sensitive, component structures of a surface acoustic wave device. The explanatory figures are only schematic representations and thus are not to scale.